OBJECTIVES:1.To perform qualitative analysis to identify metal cations2.To undergoes confirmation tests on the presence of Ag+, Cu2+and Zn2+in a mixture of metal cations.INTRODUCTION:Qualitative analysis is a very useful way on how to detect the presence of metal cations in an aqueous solution. This is ecause metal cations can only undergoes specific chemical reactions with certain reagents. For example, in this experiment we dissolve silver ion in hydrochloric acid to yeild solid ilver chloride. As the other metal cations may not react with hydrochloric acid this way, this can be used to differentiatecations that form insoluble chlorides and soluble chlorides.For part A of this experiment (experiment 1), we follow the scheme which separates metal cations into five groups according to their chemical and ohysical behaviour as listed as below:i.Analytical group l cations: Ag+, Hg2+, Pb2+-form precipitate when reacte with HClii.Analytical group ll cations: As3+,Bi3+, Cd3+, Cu2+, Hg2+, Pb2+, Sn4+-form precipitate when reacted with acidic H2Siii.Analytical group lll cations: CO3+, Fe2+, Mn2+, Ni2+, Zn2+, Al3+, Cr3+-form precipitate when reacted with H2S in NH3iv.Analytical group lv cations: Ba2+, Ca2+, Mg2+, Sr2+-form precipitate when added with (NH4)2CO3or NH4HPO4v.Analytical group v cations: Na+, K+-form soluble salts when reacted with (NH4)2CO3or NH4HPO4For part B (experiment 2) of this experiment we will make a further comfirmation test for transition metal cation which are Ag+, Cu2+and Zn2+. The confirmation tests ivolves redissolving the metal cation and followed by reprecipitating it using a confirming reagent for that particular cation.
APPARATUS AND EQUIPMENT:Centrifuge Centrifuge tubesDropper Test tubesBeaker (500 ml)Measuring cylinder (5 ml)PROCEDURE:PART A (EXPERIMENT 1)A)1.2 drops of 6M HCl is added to 1 ml of the mixture of metal cations.2.The suspension is centrifuged for 1 minute if precipitate of cloride is formed.3.1 additional drop of 6M HCl is added to the clear supernatant to check for complete precipitation. It is centrifuged again if precipitate is observed.4.The supernatant is decant in a clean test tube. The supernatant is saved for procedure B.B)1.6M of NH3is added dropwise to the solution (supernatant from part A) until it isbasic.2.The sample is placed in a boiling water bath for 2-3 minutes to remove the excess NH3.3.The volume is adjusted 2ml with distilled water and 10 drops of 6M HCl added.4.12 drops of thioacetamide is added to the solution. The solution is stirred.5.The sample is heated in a boiling water bath for 10 minutes to allow for the hydrolysis of thioacetamide producing H2S.
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